Figure 1.

(a) Schematic illustration of the synthesis of PFPE–Tris surfactants with estimated composition and (b) the corresponding FT-IR spectra. The absorbance peak at 1775 cm^–1 corresponds to the carboxylic acid C=O stretch of unreacted PFPE, whereas the absorption peak at 1675 cm^–1 represents the converted amide C=O stretch. The maximal conversion occurred when the absorbance peak of 1775 cm^–1, representing the amount of the unreacted PFPE, completely disappeared, at the feed molar ratio of 1.0. The percentage of conversion, shown as a table in (a), was estimated by the relative peak height on the FT-IR spectra. (c) Photographs of off-chip collected w/o emulsion generated by a flow-focusing droplet generator with 2 wt % unmodified PFPE or PFPE₁–Tris_1.0 dissolved in HFE-7500 as the oil phase. (d) Formation of water-in-oil-in-water (w/o/w) double emulsion by a two-step emulsification process using two integrated microfluidic chips (scale bar: 100 μm) and 2 wt % PFPE₁–Tris_1.0 in HFE-7500 as the oil phase.